[jira] [Updated] (ARROW-11763) Dict index type ALWAYS gets coerced to int32 when saving to parquet

["Antoine Pitrou (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-11763?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Antoine Pitrou updated ARROW-11763:
-----------------------------------
    Priority: Major  (was: Critical)

> Dict index type ALWAYS gets coerced to int32 when saving to parquet
> -------------------------------------------------------------------
>
>                 Key: ARROW-11763
>                 URL: https://issues.apache.org/jira/browse/ARROW-11763
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: Python
>    Affects Versions: 3.0.0
>            Reporter: ARF
>            Priority: Major
>
> On saving a pyarrow Dictionary-type column to parquet, any non-int32 index gets coerced to an int32 index without warning:
> {code:python}
> import pyarrow as pa
> from pyarrow import parquet as pq
> schema = pa.schema({
>     'foo': pa.dictionary(pa.int8(), pa.string(), ordered=False),
> })
> def make_trivial_dict_array(dict_type, value, size):
>     return 
> table = pa.Table.from_pydict({
>     'foo': pa.DictionaryArray.from_arrays(
>         pa.nulls(1, schema.field('foo').type.index_type).fill_null(0),
>         ['bar'])
> })
> pq.write_table(table, 'test_dict_int8.parquet', version='2.0', data_page_version='2.0')
> print(f"dict index type before saving to parquet: {table.schema.field('foo').type.index_type}")
> del table
> table = pq.read_table('test_dict_int8.parquet')
> print(f"dict index type after saving to parquet: {table.schema.field('foo').type.index_type}")
> {code}
> Output:
> {code}
> dict index type before saving to parquet: int8
> dict index type after saving to parquet: int32
> {code}
> While this is surprising for smaller index types, coercing an in64 index to an int32 index without warning the user seems like asking for trouble.



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